Viral marketing (known as word-of-mouth advertising when the Internet is not involved) includes any marketing strategy that encourages individuals to pass on a marketing message to others using the social network of the Internet. This creates the potential for exponential growth of the marketing message, as an individual passes on the message to his friends, those friends pass it on to their friends, and so on. Viral marking, so called because it spreads similar to a virus epidemic, exploits pre-existing social networks to produce exponential increases in brand awareness. Viral marketing harnesses the network effect of the Internet.
Viral marketing is popular because such as marketing campaign is relatively easy to implement, has a relatively low cost, and yields a high and rapid response rate. Thus, the strength of viral marketing lies in its ability to obtain a large number of interested people at a low cost. Viral marketing is more powerful that traditional third-party advertising because it implies an endorsement from a friend or acquaintance.
One popular forum for viral marketing is online social networks. Online social networks are communities on the Internet where people can come together to exchange information, ideas, and opinions. These online social networks (such as MSN® Spaces) are rich with user-created text content, imported pictures, and music. Many online social networks are quite large in scale. For example, one online social network has more than 58 million users. These users interconnect with each other, which builds up a very rich and useful social network for each user. A user's social network is his compilation of online friends. This personal social network may contain hundreds or even thousands of other users, along with complex and often unique links between the user and a friend. For example, a link between the users and an online friend may range from a casual acquaintance to close family member. The link may not even be user initiated; it may simply be another user in the community viewing the user's blog.
One problem when implementing a viral marketing plan is finding a set of influential people from a group of people. More specifically, an advertiser may be unable to send its message to all members of an online social network. However, there are connections between these people. If one person sees the advertising, he may tell his friends. Thus, it is desirable for the advertiser to determine a select number of people in the social network who will maximize the number of people who ultimately receive the advertising message. The problem becomes how to best select these so called influential people (or influencers) in the social network.
One naive method is to select a certain number of people having the most friends. However, people selected by this method frequently are in the same social community and circle of friends and only cover a portion of the entire social network. Therefore, this method usually does not reach the maximum coverage. Another of finding influencers is to try all combinations of a certain number of people that will maximize the spreading of the advertising message. However, this requires an inordinate amount of computation time, and therefore is not a feasible alternative.